Nineteen strains of gram-negative organisms representing 10 species, , and the so-called were investigated for cytochromes and respiratory quinones. Phenotypical variation of cytochrome and quinone contents was checked using cells grown with oxygen and fumarate as alternative electron acceptors. The cytochromes were detected by difference spectra of briefly sonicated cells at room temperature, and the quinones were determined in lipid extracts by difference spectrophotometry and partly by thin-layer chromatography. In contrast to other conventional groups of chemo-organotrophic, gram-negative bacteria that have been found to be highly homogeneous with respect to the respiratory chain components, the organisms investigated here may be divided into three categories by their respiratory quinones, namely (i) bacteria containing desmethylmenaquinone as sole respiratory quinone— (in part), (ii) bacteria containing both ubiquinone and desmethylmenaquinone— (in part), and (iii) bacteria containing only ubiquinone—, so-called , and The data presented may contribute to further characterization, independent of growth factor requirements, of the taxonomic entities investigated. In the absence of information on deoxyribonucleic acid relatedness between the organisms under study, a provisional reclassification of and related taxa on the basis of respiratory quinones is discussed.


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